1. Field of the Invention
This invention relates to storage media library subsystems as frequently found in computer mass storage applications. More specifically, this invention comprises improvements and simplifications that enable reductions in the size and complexity of storage media library subsystems.
2. Statement of the Problem
Storage library subsystems are commonplace in high volume computer storage applications. Such library subsystems permit the use of lower cost per byte storage devices (such as high density tape storage) but retain automated access to storage media through the use of robotic retrieval mechanisms. Robotic mechanisms in this context typically constitute an arm capable of moving in three dimensions. The arm moves vertically to align itself with storage media cartridges at various heights in inventory storage of the library. The arm has a gripping hand attached to its end that extends horizontally to permit the hand to grip or release a media cartridge. The typical arm also rotates to position itself as required to retrieve a particular media cartridge or to deposit a previously retrieved media cartridge back into inventory.
Large numbers of storage media cartridges are stored in inventoried locations within the library subsystem. Robotic arm mechanisms store and retrieve the media cartridges in the inventoried locations as requested by a host computer system. On request from a host computer system, the library robotic mechanism retrieves a required storage media cartridge from an inventoried location, moves the media cartridge to a read/write device for processing of the media cartridge and deposits the media cartridge in the read/write device. Similarly, on command from a host computer system, the robotic arm retrieves the media cartridge from the read/write device and returns the media cartridge to the inventoried location for storage.
Library subsystems have become an important component in Hierarchical Storage Management (hereafter HSM) subsystems. HSM subsystems utilize control mechanisms and algorithms to provide mass storage of information across a broad range of price/performance storage media. At the high end of the performance spectrum, rotating disks often referred to as Direct Access Storage Devices (hereafter DASD) provide rapid random access to a relatively small volume of stored information. At the lower end of the performance spectrum, devices such as library subsystems provide access to much larger volumes of stored information but are substantially slower to access. In general, the higher speed lower volume DASD devices are more costly per stored byte than are the slower speed higher volume tape storage devices. HSM subsystems control storage devices of many types; higher speed lower density and higher cost, through lower speed higher density and lower cost. HSM subsystems manage the collection of storage devices so that a host computer system views the HSM subsystem as a single, large, seamless linear array of storage rather than individual storage devices requiring different control algorithms and timing.
HSM subsystems automatically migrate information from higher cost higher speed devices to lower cost lower speed devices as space and utilization so require. Infrequently accessed information stored on higher speed DASD is migrated by HSM control logic to slower speed lower cost per byte storage devices such as tape or optical disk. Conversely, frequently accessed information stored on lower speed tape devices is migrated by the HSM control logic to higher speed DASD. This migration of information is done in a manner which is hidden from the user at a host computer system and maintains the appearance at the host computer interface of a single, large, seamless linear array of storage. The computer user will typically not require specific knowledge of the location of the requested information. The HSM subsystem locates and retrieves the desired information from whichever medium has it currently stored. The only observable difference to a user at a host computer system is the speed with which the data is accessed. Frequently accessed information will be available more rapidly than less frequently accessed information.
Despite "downsizing" and "client/server model" networking of computer applications in the computer industry, library subsystems have remained large and complex. The size and costs of such library subsystems have been a substantial factor in precluding them from new markets. In particular, HSM subsystems are a fraction of the size and mechanical complexity of current library storage subsystems. This size and complexity has precluded use of current library subsystems in "downsized" networked computing environments. Several problems with current library subsystems are factors in their large size and complexity.
The size of current library subsystems is in part due to the capacity of storage media utilized. Lower density storage media requires a larger number of storage media cartridges to attain a useful total storage capacity for the library. This larger number of storage media cartridges requires, in turn, a broader range of motion for the robotics utilized to retrieve the media cartridges. This broad range of motion (usually in three dimensions) coupled with the precise positioning required to grip a media cartridge has been the impetus for the complex robotic mechanisms found in prior storage library subsystem designs. The STK ACS4400 library subsystem, as an example, utilizes a complex computerized vision system to precisely position a large robotic arm over a broad range of motion in three dimensions to grip a small storage media cartridge.
Another complexity of current library subsystems stems from the need for maintaining an accurate inventory of the library contents. Some library subsystems of prior design permit unlimited operator access to cartridges inventoried within the library. Human operator access is the only practical approach to mass loading of the room sized device of prior designs. Prior designs of storage libraries require significant time following such human operator access to verify the library inventory. The aforementioned computer vision system (or in other designs, a bar code reader) attached to the robotic arm mechanism is operated to re-read the labels of every storage media cartridge following such human operator access. During this time consuming inventory process the library subsystem is unavailable.
3. Solution to the Problem
The present invention solves the above problems and others and advances the art by providing a smaller simpler library subsystem. The smaller size, reduced complexity and the resulting reduced costs make the library subsystem of the present invention an appropriate device for HSM subsystems in the "downsized" "client/server model" network computing environment. In one exemplary embodiment of the present invention, the HSM controller subsystem and the associated storage media devices may be integrated within the same small cabinet of the library subsystem of the present invention.
The present invention utilizes high density storage media cartridges (such as high density tape cartridges) to reduce the total number of media cartridges required to achieve a useful library subsystem storage capacity. In addition, the media cartridges are stored in inventory slots in Cartridge Access Magazines (hereafter CAMs). The CAMs store several media cartridges in slots aligned in a vertical column. The CAMs hang on the facets of a multi-sided cylinder and are lifted off to remove the CAM with its media cartridges from the library subsystem. The multi-sided cylinder is rotatable such that any one of the magazines hanging on a face of the cylinder may be positioned in the plane of the robotic arm. The slots in the CAMs are angled such that the rear part of the slot is tilted downward relative to the front part. This tilt helps retain the cartridges within the slots of the CAM as the carousel is rotated. This combination of a reduced number of higher density storage media cartridges and the rotating carousel reduces the range of motion required of the robotic mechanisms to reach each media cartridge.
In the simplest embodiment of the present invention, the robotic arm mechanism need move in only two dimensions to reach every media cartridge as well as the read/write devices. The robotic arm is controllably moved in the vertical dimension to position itself at each media cartridge slot in a CAM. The gripping hand at the end of the arm is extended from the arm in a horizontal plane to permit the hand to grip and extract a media cartridge or to deposit and release a media cartridge. The rotation of the carousel provides the third dimension of motion. This simplified two dimensional motion of the robotic arm coupled with the reduced range of motion to reach each media cartridge enables reduced complexity in the design of the robotic mechanism. Vision systems as used in past designs are no longer required to position the robotic arm mechanism. Instead, simple mechanical detents or servo motors are used to move the robotic arm to each storage media cartridge inventory location.
Past designs also used a vision system to inventory media cartridges stored in the library subsystem. A simpler bar code scanning device attached to the robotic arm replaces the complex vision systems of past designs. This bar code scanner provides a simple mechanism to automatically control the media cartridge inventory within the library subsystem.
Other embodiments of the present invention contemplate a single robotic arm capable of moving to one of multiple rotating carousels. This motion of the robotic arm remains simpler than past designs in that simple mechanical detents or servo motors can easily position the robotic arm. The need for complex vision systems to accurately position the robotic arm to a single media cartridge is eliminated in favor of simpler robotic arm motion.
Another feature of the present invention is a Cartridge Access Port (hereafter CAP). The CAP is an access port with a door that is controllably lockable by the control logic of the library subsystem. Unlike past designs, the storage library of the present invention is intended to eliminate human operator access to the inventory locations within the library (except in an "off-line" service mode). The intended mode of operator access to the inventoried media cartridges is through the CAP. One of the several CAMs hanging from the carousel is reserved for operator access through the CAP. No media cartridges are stored in the reserved CAM for inventory storage within the library. A human operator requests that the library subsystem retrieve a particular media cartridge (or group of media cartridges) for removal from the library subsystem. In response, the library subsystem rotates the carousel and activates the robotic arm to fetch the desired media cartridge. Next, the carousel is rotated to align the reserved CAM with the robotic arm and the retrieved media cartridge is deposited in an empty position of the reserved CAM. The carousel is then rotated so that the reserved CAM is aligned with the CAP. A lockable door on the CAP is then unlocked by the library subsystem to permit the operator to remove the retrieved media cartridge. In a similar manner, the operator may request that the CAP door be unlocked so that the reserved CAM may be filled with new media cartridges to be added to the library inventory. The CAP door is again locked after the operator indicates the reserved CAM is filled and the library subsystem moves the new media cartridges from the reserved CAM into empty inventory locations of the non-reserved CAMs. The apparatus and methods of the present invention limit operator access to the cartridges without the addition of another mechanism as found in some prior designs. The operator accesses the cartridges in the carousel directly through the unlocked CAP door without the addition of another transfer mechanism as found in prior designs. However, that access is limited to the cartridges in the reserved CAM aligned with the CAP while the CAP door is unlocked. The present invention assures the integrity of the library inventory by limiting human operator access to the storage media cartridges. This limited operator access reduces the need for time consuming inventory checking as recited in prior designs following human operator access.
Another feature of the present invention is manifested in the placement of the carousel with respect to the read/write devices. The read/write devices are placed under the carousel aligned with the vertical plane of movement of the robotic arm mechanism. This positioning permits the robotic arm to move media cartridges between their inventoried locations in the CAMs hanging on the cylindrical carousel with only the simple two dimensional motions of the arm as described above. This design also improves the location of the CAMs on the carousel relative the height of an average operator as well as the weight distribution of components within the library subsystem.
Alternative exemplary embodiments of the present invention add limited simple rotational movement of the robotic arm. Such simple rotation of the robotic arm enables one robotic arm to rotate between two or more positions. Each such rotational position is aligned to service CAMs on a different carousel. This rotational movement permits a single robotic arm to service multiple carousels while retaining simplicity of robotic motion as compared to the broad range of motion required of prior designs.
Yet another feature of the present invention is the integration of Local Media Storage racks within the cabinet panels of the storage library. This Local Media Storage, (hereafter called LMS), provides a convenient storage area for CAMs or storage media cartridges which may be frequently requested by host computer systems. A manually operated bar code reader connected to the library subsystem control electronics provides semi-automatic inventory management of media cartridges and CAMs stored outside the robot controlled inventoried locations of the library subsystem. The library control electronics can inform the operator of the probability that a desired media cartridge or CAM is in the LMS racks. This semi-automatic location of media cartridges and CAMs assists the human operator in rapidly locating a media cartridge or CAM requested by a host computer system.
The CAMs and robotic gripping hand of the present invention permits the use of various types of storage media cartridges. Tape cartridges, CDROM cartridges, rewritable optical disc cartridges, Write Once Read Many disk cartridges (hereafter referred to as WORM cartridges), miniature disk array cartridges, and other potential storage media cartridges are manipulated by the robotics of the present invention and inventoried in slots of CAMs of the storage library subsystem. The storage library subsystem of the present invention includes a gripper hand capable of gripping such a variety of media cartridges. Furthermore, the present invention comprises read/write devices to manipulate the various cartridge and media formats. Additionally, the physical orientation of the media cartridges within the slots of the CAMs may be varied with an appropriately adapted gripper hand to permit a broader variety in the types of media cartridges stored within the library subsystem.
The simple design and small size of the storage library of the present invention enables cost effective, high capacity, low cost information storage libraries to be used in HSM subsystems of current client/server network computing environments.